Pigs familiar with duckweed readily accept another unfamiliar green feed, Leucaena leucocephala

Dam Van Tien

Department of Animal Physiology and Behaviour, Faculty of Animal Science,
Hue University of Agriculture and Forestry, Hue City, Vietnam
tiendamvan@dng.vnn.vn

Abstract

This study was undertaken to determine if Large White and Mong Cai pigs that were familiar with duckweed would readily accept another green feed. The feed chosen for the test was the fresh leaf of Leucaena leucocephala. The experiment showed that all pigs that were familiar with duckweed started eating the new, unfamiliar feed immediately on the first occasion it was offered to them. The naive control animals totally rejected the new feed to which they were exposed.

It is concluded that, at least under specific conditions, familiarity with a certain feedstuff can be generalized to another feedstuff.

Introduction

Cheap feed supplements may be used in order to improve animal production during the dry season in tropical countries. However, unfamiliar new feeds, such as agricultural by-products, are often not readily accepted, and instead are initially rejected by the animals. There are practical ways to adapt livestock to new feeds, thus promoting feed intake. Our research with small ruminants and pigs has demonstrated some effective techniques, such as the use of additives with a familiar odour or flavour (Tien et al 1999; Tien and Ha 2000), the training of animals to ingest novel feeds in their early lives while they are with their mothers or other experienced animals (Lobato et al 1980, Tien and Ha 2000), the offering of new feeds to mothers during the gestation period in order to imprint their offspring to readily accept the new feeds (Tien et al, unpublished data) or making use of goat bipedal stance behaviour (Malechek and Provenza 1981; Tien and Beynen unpublished data). The present study was designed to test if experience with a certain type of feed affects the acceptance of another novel, but comparable feedstuff. More specifically, the question addressed was whether pigs that had been exposed to duckweed until one month before testing would show a more rapid intake of another green feed, Leucaena leucocephala, during acceptance testing.

Materials ansd methods

Experimental preparation

The test was conducted at the Pig Breeding Station of Quang Nam Province, Vietnam. Six exotic Large White and six native Mong Cai pigs were randomly allocated to two groups: with ("experienced") or without ("naive") experience with duckweed. The pigs had been used in a previous experiment on in utero learning. All pigs were fed the diet commonly used at the Pig Breeding Station. Three months before the tests the "experienced" pigs were also offered duckweed: 500 g per day for the Large White and 300 g for the Mong Cai genotype. The "naïve" pigs did not receive duckweed. Thus, there were four experimental groups each consisting of three animals: experienced Large White, naïve Large White, experienced Mong Cai and naïve Mong Cai. At the time of testing the pigs were aged about 6 months and had not been fed duckweed for a period of one month. The test periods lasted 5 days for the Large White pigs and 11 days for the Mong Cai pigs. The duration of the test period was based on maximum intake of the test feed. During the tests both experienced and naive pigs were offered Leucaena leucocephala.

Testing procedures

Before the tests with the new feed, Leucaena leucocephala, all pigs were exposed to the testing environment and routine for 3 days. All animals were adapted to the testing facilities and during adaptation were fed sweet potato leaves only. They had no contact with either duckweed or Leucaena leucocephala..

The test was carried out each day for each individual pig and lasted 40 minutes, and was divided into four periods of 10 minutes each. Individual intakes for each period, and the total intake for the 40 minute period were calculated immediately after the test had finished. After each time interval, the feeder was removed and another feeder with the same size and color was immediately put in place. The test feed was offered ad libitum throughout.

After an overnight fast in the holding pen, all pigs were offered fresh leaves of Leucaena leucocephala and individual intake was sequentially measured for each 10 minute period over the 40 minute test period. The new feed was placed on a woven bamboo feeder and amounted to 300 g for the Large White pigs and 150 g for the Mong Cai. The feeders were thoroughly cleaned, rinsed and air-dried after each 40 minute test, after which the pigs were allowed access to their normal diet.

Results

Table 1 shows the mean intake of Leucaena leucocephala by the Large White and Mong Cai pigs in the "experienced" groups over 5 and 11 days of testing, respectively. Both groups of experienced pigs showed interest in the supplement from day 1 and started to ingest the feed on that day without any signs of feed neophobia. The experienced Large White pigs ate more Leucaena leucocephala than did the Mong Cai pigs. During the test, the naïve animals of each genotype did not eat any feed.

 

The intake of animals in both experienced groups decreased from the first interval (0-10 minutes) to last interval (30-40 minutes) and, in general, had a lowest intake in the final period. It would appear that offering Leucaena Leucocephala in a 40-minute test period was sufficiently long for the pigs to ingest an appreciable amount of the supplement.

Discussion

According to Preston (2000) it is important to facilitate the introduction of new, locally available feed resources to partially replace expensive commercial feeds. However, feed neophobia occurs when a new supplement is given to animals (Tien and Ha 1998; Tien et al 1999, Tien 2000; Tien  2001). The fact that the naïve Large White and Mong Cai pigs in this experiment rejected the supplement of Leucaena leucocephala supports the concept of feed neophobia.

In a previous study (Tien et al, unpublished data) it was demonstrated that if during pregnancy a sow was given a new feed in the form of duckweed, its offspring would quickly accept this new feed in the post-weaning period. It was hypothesized that such pre-conditioning may be generalized to another new feed. This was confirmed by the fact that the experienced pigs familiar with duckweed quickly accepted the comparable, but new feed, given in the form of Leucaena leucocephala. The mean intake of the Large White pigs reached the highest value on day 4, and that of the Mong Cai pigs was highest on day 11. The naive pigs did not eat the new feed at all, whereas the experienced pigs accepted it on the first day of exposure. It is suggested that the pre-conditioning with duckweed had generalized to the new feed, i.e. Leucaena leucocephala. The present finding may be considered to be the first evidence for a generalization of feed acceptance, but this needs further study in pigs and also in other kinds of livestock.

The use of trees such as Leucaena leucocephala in mixed farming systems in Vietnam is appropriate, as these trees are good for the environment, while their foliage and shrubs may serve as feed for ruminants (Devendra and Burns 1983; Shelton et al 1994). A study carried out in Vietnam by Nhan (2000) indicated that Leucaena leucocephala foliage, which is rich in protein, can be used as the basal diet for goats. However, there are no data showing that it can be used as a supplementary feed for monogastric animals. Because naive livestock may reject the new feed for quite a long period, both the farmers and Vietnamese researchers may be led to believe that the legume foliage is not suitable as animal feed (Tien 2001). However, the recommendation derived from this study is that Leucaena leucocephala can serve as supplementary feed for pigs and that its acceptance can be improved by pre-feeding of the pigs with duckweed.

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